1. Field of the Invention
The present invention relates to wireless sensor networks that includes a multiplicity of individual sensor nodes and more particularly to a self-organization wireless receiver and method of utilizing such a receiver in an ultra-wideband (UWB) radio network.
2. Description of Related Art
Wireless sensor networks (WSNs) have become increasingly popular in military and civilian applications such as surveillance, monitoring, disaster recovery, home automation and many others. In a wireless sensor network, a large population of sensor nodes can be scattered in an inaccessible area to detect a physical phenomenon and process/transfer the information through wireless links to an expected destination. Due to the dense deployment of sensor nodes in such remote areas, the individual nodes are designed to have a small form factor, be light weight, provide long service with a limited energy source, and be inexpensive so they can be deployed in large numbers. The state of the art wireless sensor networks typically use conventional spread spectrum, or narrowband RF physical links. When WSN nodes are scattered in harsh RF environments, even the most advanced commercial off the shelf (COTS) radio faces significant problems at high data rate communications between the sensor nodes.
Unlike conventional RF communications, ultra-wideband transceivers use carrierless, short duration (pico second to nano second) pulses to transmit and receive information. The short duration of UWB pulses spreads their energy across a wide range of frequencies from near DC to several Gigahertz. Such a large bandwidth provides high capacity and low probability of detection properties for UWB communication systems. Using UWB technology for inter-node communication of WSNs not only offers small form factors but also provides high performance for communication over the wireless channels in spite of multipath distortions.
Furthermore, transmission of short duration UWB pulses requires much lower power compared to strong narrowband signal transmission. In UWB-based WSNs, nodes can only communicate with their close-by neighbors due to low transmission power and avoid the inter-node interference issue that exists in narrowband techniques. Despite all the benefits that UWB technology offers to the design of WSNs, it can also create a unique set of challenges. Employing the low powered UWB pulses for inter-node communications introduces the scalability problem in WSNs. As the distance between nodes or the number of nodes increases, weak UWB pulses cannot transfer the information between the nodes properly. In addition, the short duration of UWB pulses introduces a major challenge in time synchronization for sensor nodes in a wireless network. In order to synchronize sub-nanosecond pulses, very high-speed ADC components are needed.
Another problem with using UWB technology for wireless sensor networks is the performance degradation due to interference from strong narrowband signals that share the spectrum with low powered UWB pulses. Moreover, detection of UWB pulses is commonly performed using classical matched filtering technique. Therefore, where the received signal is correlated with a UWB pulse template, wireless channel effects (such as multipath) on the received signal can significantly degrade the detection process due to low correlation between the predefined template and the distorted received signal.
The main design challenges in WSNs can be categorized into the following areas:
                Scalability: As the number of sensor nodes in a wireless network increases, scalability imposes difficulties in transferring data. In order to send information to far away nodes, signals with higher transmission power is typically employed, which can cause inter-node interference or a multi-hop approach needs to be considered.        Power conservation: The nodes in wireless sensor networks have limited energy resources, so to extend the lifetime of the entire network, power conservation in individual nodes is of significant importance. In WSNs, radio communications is the major consumer of energy. Hence, minimizing the radio transmission power or avoiding the unnecessary communications can considerably save power in sensor nodes.        Synchronization: In radio communications between sensor nodes of a WSN, sensors continuously listen to transmissions and consume power if they are not time synchronized with each other. While global synchronization is unrealistic due to the large sensor population, node-by-node synchronization becomes a necessity in WSN design.        Channel estimation: Channel estimation plays a critical role in WSNs, since sensor nodes communicate over wireless channels and have to overcome the effects of wireless link, such as noise, multipath effect, intentional jamming and inter-node interference. Estimating the wireless link between a specific transmitter and receiver pair provides directionality and reliable data transfer between the nodes.        
Accordingly, a need exists for a UWB approach that facilitates self-organization of individual nodes with respect to power efficiency, scalability, channel estimation, and node synchronization in WSNs. The present invention is directed to such a need.